The
Neoproterozoic Era is the unit of geologic time from
1,000 to 541 million years ago.[1]
It is the last era of the
PrecambrianPrecambrian Supereon and the Proterozoic
Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran
Periods. It is preceded by the
Mesoproterozoic era and succeeded by
the
PaleozoicPaleozoic era.
The most severe glaciation known in the geologic record occurred
during the Cryogenian, when ice sheets reached the equator and formed
a possible "Snowball Earth".
The earliest fossils of multicellular life are found in the Ediacaran,
including the Ediacarans, which were the earliest animals.
According to Rino and co-workers, the sum of the continental crust
formed in the
Pan-African orogenyPan-African orogeny and the
Grenville orogenyGrenville orogeny makes the
Neoproterozoic the period of Earth's history that has produced most
continental crust.[2]

Geology[edit]
At the onset of the
Neoproterozoic the supercontinent Rodinia, which
had assembled during the late Mesoproterozoic, straddled the equator.
During the Tonian, rifting commenced which broke
RodiniaRodinia into a number
of individual land masses.
Possibly as a consequence of the low-latitude position of most
continents, several large-scale glacial events occurred during the
Neoproterozoic Era including the
Sturtian and
MarinoanMarinoan glaciations of
the
Cryogenian Period.
These glaciations are believed to have been so severe that there were
ice sheets at the equator—a state known as the "Snowball Earth".
Subdivisions[edit]
Russian geologists divide the
Neoproterozoic of
SiberiaSiberia into the
Baikalian from 850 to 650 Ma (loosely equivalent to the Cryogenian),
which follows the Mayanian, from 1000 to 850 Ma, then the
Aimchanian.[3]
Paleobiology[edit]
Main article: Ediacara biota
The idea of the
Neoproterozoic Era was introduced in the 1960s.
Nineteenth-century paleontologists set the start of multicelled life
at the first appearance of hard-shelled animals called trilobites and
archeocyathid sponges. This set the beginning of the
CambrianCambrian Period.
In the early 20th century, paleontologists started finding fossils of
multicellular animals that predated the start of the Cambrian. A
complex fauna was found in South West
AfricaAfrica in the 1920s but was
inaccurately dated. Another fauna was found in South Australia in the
1940s but was not thoroughly examined until the late 1950s. Other
possible early fossils were found in Russia, England, Canada, and
elsewhere (see
EdiacaranEdiacaran biota). Some were determined to be
pseudofossils, but others were revealed to be members of rather
complex biotas that are still poorly understood. At least 25 regions
worldwide yielded metazoan fossils older than the classical Cambrian
boundary at 541 million years ago.[4]
A few of the early animals appear possibly to be ancestors of modern
animals. Most fall into ambiguous groups of frond-like organisms;
discoids that might be holdfasts for stalked organisms ("medusoids");
mattress-like forms; small calcareous tubes; and armored animals of
unknown provenance.
These were most commonly known as
Vendian biotaVendian biota until the formal
naming of the Period, and are currently known as
EdiacaranEdiacaran Period
biota. Most were soft bodied. The relationships, if any, to modern
forms are obscure. Some paleontologists relate many or most of these
forms to modern animals. Others acknowledge a few possible or even
likely relationships but feel that most of the
EdiacaranEdiacaran forms are
representatives of unknown animal types.
In addition to
EdiacaranEdiacaran biota, two other types of biota were
discovered in China (the
Doushantuo Formation and Hainan Formation).
Terminal period[edit]
Main article: Ediacaran
The nomenclature for the terminal Period of the
Neoproterozoic Era has
been unstable. Russian and Nordic geologists referred to the last
period of the
Neoproterozoic as the Vendian, while Chinese geologists
referred to it as the Sinian, and most Australians and North Americans
used the name Ediacaran.
However, in 2004, the International Union of Geological Sciences
ratified the
EdiacaranEdiacaran Period to be a geological age of the
Neoproterozoic, ranging from 635 to 541 million years ago.[1] The
EdiacaranEdiacaran Period boundaries are the only
PrecambrianPrecambrian boundaries
defined by biologic Global Boundary Stratotype Section and Points,
rather than the absolute Global Standard Stratigraphic Ages.
See also[edit]